Coloured filters can simulate colour deficiency in normal vision but cannot compensate for congenital colour vision deficiency

Red-green colour vision deficiency (CVD) affects ~ 4% of Caucasians. Notch filters exist to simulate CVD when worn by colour vision normal (CVN) observers (simulation tools), or to improve colour discrimination when worn by CVD observers (compensation tools). The current study assesses effects of simulation (Variantor) and compensation (EnChroma) filters on performance in a variety of tasks. Experiments were conducted on 20 CVN and 16 CVD participants under no-filter and filter conditions (5 CVN used Variantor; 15 CVN and 16 CVD used EnChroma). Participants were tested on Ishihara and Farnsworth-Munsell 100 hue tests, CVA-UMinho colour discrimination and colour naming tasks and a board-game colour-sorting task. Repeated-measures ANOVAs found Variantor filters to significantly worsen CVN performance, mimicking protanopia. Mixed-model and repeated-measures ANOVAs demonstrate that EnChroma filters do not significantly enhance performance in CVD observers. Key EnChroma results were replicated in 8 CVD children (Ishihara test) and a sub-sample of 6 CVD adults (CVA-UMinho colour discrimination and colour naming tasks) for a smaller stimulus size. Pattern similarity exists across hue for discrimination thresholds and naming errors. Variantor filters are effective at mimicking congenital colour vision defects in CVN observers for all tasks, however EnChroma filters do not significantly compensate for CVD in any.


Repeatability analysis
. Mean task scores across two runs, with and without filters for British participants. Means ± 1 standard error of the mean (SEM) scores (first and second run) used for the repeatability analyses.

Enchroma effect on CVN observers Laboratory analyses
There was only a single laboratory effect on the laboratory analyses provided in the main text. For the CVA-UMinho discrimination task (5°), a significant laboratory*hue*participant group interaction contributing to lower order effects was found. A Tukey posthoc comparison analysis revealed that significant differences originate from differences between the CVD participant group data (UK versus Portugal) for hues 4.66°, 184.66° and 196° (hues at and near Protan axes) with P = 0.003, P = 0.004 and P = 0.022, respectively). Higher protan thresholds for the Portuguese CVD sample are expected based on the characteristics of the CVD Portuguese group (3 protanopes, 2 protanomals, 0 deuteranopes and 2 deuteranomals) in comparison to the British group (1 protanope, 2 protanomals, 4 deuteranopes and 2 deuteranomals). No differences between the two laboratories for any hue was found for CVN adults (all P = 1.000). The lack of significant differences across CVN samples justifies collapsing data from the two laboratory samples for the main analysis.

CVA-UMinho discrimination task
To investigate whether different trends in wearing EnChroma filters might occur for CVN versus CVD groups, differences in thresholds (i.e., filter minus no-filter) with 5° stimuli were compared, with hue as the within-subjects factor, and participant group as the between-group factor. There was no significant main effect of group (P = 0.644), or significant interaction between group and hue (P = 0.330). With less stringent posthoc testing (using Fisher LSD), significant differential effects were found between CVD and CVN groups for the hue at 162° next to a deutan axis (P = 0.005). EnChroma filters made CVD participants relatively better (difference of 0.00461±0.00126), than CVN participants (difference of 0.00043±0.00130).

Colour Naming task
Although colour naming characteristics across languages vary 55,63 , naming effects of

EnChroma filters for CVN versus CVD groups (combined across our British and
Portuguese participants) could be statistically analysed as variance existed for all BCTs, filter conditions and CVN and CVD groups. A three-way mixed model ANOVA with filter (no-filter, EnChroma) and BCT (green, blue, pink, purple, orange and brown) as within- As with CVA-UMinho discrimination thresholds, we investigated whether different trends in filter effects occurred for CVN, versus CVD groups. Differences in hit-scores (i.e., nofilter minus filter) were compared using an ANOVA, with hue as the within-subjects factor and participant group as the between-group factor. No significant effects of group (P = 0.325), or interaction between group and hue (P = 0.351), were found. Less stringent posthoc testing (using Fisher LSD) found significant differential effects between CVD and CVN groups for hue at 306° (P = 0.002), commonly perceived as "pink". At this hue angle, CVD participants improved in naming performance with filters (by 10.07±3.66%), but CVN participants performed worse (by 9.26±3.78%).

Modal BCT
Used BCT red green blue yellow pink purple grey orange brown black white     Table S14. Mean CVD naming hit percentages using CVA-UMinho test with and without EnChroma for the loose criterion 1° stimuli. Naming task hit percentages for CVD participants without using (outside brackets) and using EnChroma (inside brackets) for the loose criterion. Notes: Used BCT refers to those BCT used by CVD participants (EnChroma sample). Loose BCT refers to all responses given by CVN participants (computed using both Variantor and EnChroma sample) without filters. Main diagonal (bold) represents hit scores (naming with one of the responses used by any of the CVN without filters) by CVD not using (outside brackets) or using EnChroma (inside brackets). Other values represent errors (naming with a BCT that is not a response of any CVN without filters). Blank cells represent 0±0 (0±0) values. Used BCT  red  green  blue  yellow  pink  purple  grey  orange  brown  black  white